What would you like to know about this please?
You mean can you stop him complaining?
To whom is he complaining?
There isn't any way of preventing a person from complaining. Some people are just moaners by design. If they making allegations to officialdom then there is a claim in harassment but there has to be a large number of allegations that you can disprove.
If it is just that he is being a bit whingy over a garden fence then Im afraid that is not actionable in law.
You can always just ignore him. Usually that works with malingerers. They just want people to dance attendance on them.
Can I clarify anything for you?